Fossil fuels currently power the majority of modern internal combustion engines (ICEs). But hydro-carbon fuels derived from petroleum and other stocks are a scarce resource and the extensive use of such fuels in automobiles is believed by many persons to contribute to undesirable climate change due to the byproducts of combustion. Therefore, there is tremendous pressure to increase the efficiency of the modern internal combustion engine. The demand for increased efficiency is also driven by government quotas, mandates and taxes regarding fuel consumption and CO2 emissions. And this is occurring simultaneously with increasing demands to enhance safety of automobiles, which often increases weight to the detriment of efficiency.
Current steps employed to increase efficiency of ICEs can add considerable cost and complexity while decreasing reliability, power and drivability. For example, there have been numerous attempts to add adjustability to the operation of the intake and/or exhaust valves during the operating cycles of ICEs.
Traditionally the intake and exhaust valves (also referred to as poppet valves) of an ICE have been actuated by one or more camshafts which are mechanically driven from the ICE crankshaft at half engine speed, thereby operating the valves in synchronism with the ICE rotation, and in a fixed phase with one another. It is also known to substitute rotary valves for poppet valves, again mechanically driving the valves from the crankshaft and rigidly slaving the valve operation to ICE crankshaft rotation.
The camshaft profile defines timing of the valve open/close movements. Camshaft design is an exercise in tradeoffs because a given camshaft profile can only be optimized for a very narrow range of crankshaft speeds (measured in rotations per minute (RPMs)). Thus compromises must be made to facilitate easy starting and operation over a broad range of speeds, and these compromises decrease the overall efficiency of the ICE and require great complexity.
Moreover, the mechanical camshaft has a fixed amount of valve movement (lift) and time that the valve is open (degrees of duration). The opening times and closing times of the valves are also rigidly fixed by the mechanical drive systems and camshaft profile. Adding additional camshafts and valves allows optimizing one camshaft/valve system for low speed and the other for high speed, but this still has to be compromised in order to allow easy starting and a broad range of operating speeds.
It is further known that the camshaft(s) may be rotationally advanced and/or retarded with respect to the crankshaft rotational position by various means such as hydraulically bi-directionally rotating the drive mechanism of the camshaft. This is referred to as “phasing” the cam. Phasing facilitates operation of the ICE at various times, temperatures, conditions, loads and altitudes. As is also well known, this form of making adjustments to engine timing may be enhanced further by adjusting valve lift in a variety of ways. However, such systems suffer from heightened complexity. For example, the manufacturing precision required of all of the many parts is heightened, which adds cost and points of failure.
Also, the precise viscosity of the hydraulic fluid required to operate the many parts further adds to costs and expense of maintenance. It is desirable to have the valve actuation systems use engine oil as the required hydraulic fluid for operation. But, even oils meeting current API and SAE specifications may not be precise enough viscosity to meet the requirements of these applications. This necessitates specialized lubricants be used, which limits the motorist's ability to acquire top-up oil, perform their own oil changes, and adds to the cost of automobile maintenance.
Further problems with the camshaft phasing technologies described above are that valve timing, valve duration and valve lift are fixed. These parameters can only be changed slightly and such change requires expensive and complex technology.
Various attempts have been made to overcome the shortcomings of the technologies discussed above and achieve independent valve operating times and duration, most with only partial success. Some, for instance demonstrate valve operation independent of crankshaft position, but suffer from problems inherent to hydraulic operation of the valves due to the cycling of the valve from open to closed in an uncontrolled manner. Such operation is particularly damaging to the valve and valve seat upon the valve closing. Also, the length of stroke of the valve movement (i.e., valve lift) is not variable in this mechanism. Others use an electronically controlled hydraulic system for variable actuation of the inlet and/or exhaust valves of the engine. They use a standard camshaft that is mechanically slaved to the crankshaft of an ICE, but with the additional disposition of an electronically controlled hydraulic lifter between the camshaft and the valve. Through electronic control of the hydraulic fluid into and out of the lifter, the opening and closing time of the valve and the lift of the valve can be controlled to some extent. However, this arrangement is limited to the operation of the mechanically slaved camshaft and, for instance, cannot command a valve to open at maximum lift for a long duration, or at a different time than the camshaft scheduled opening time.
Attempts have been made to make ICE valve operation independent of crankshaft positioning by driving the valves open and shut with direct hydraulic pressure that is applied by electrically controlled valve means. An electrical command is sent by control unit, which receives input from engine and associated system sensors. However, such systems still suffer from significant drawbacks as will be explained below. Some attempt to minimize hydraulic valve controls for the ICE valves and the operation of an ICE using hydraulically operated ICE valves. High hydraulic pressure is used to push the valve in one direction while low hydraulic pressure combines with a balancing spring to cushion and stop the ICE valve movement. The multiple hydraulic valve controls per ICE valve, balancing springs and multiple hydraulic pressures add unreasonable complexity to the system. Further, it is difficult to control valve lift variations with this system. Another approach to hydraulically operated valves in an ICE charges an upper chamber with fluid to close the ICE valve and a lower chamber to open the valve. One drawback with this mode of moving an ICE valve is that the hydraulic fluid control valves can only be in open or closed states. A “throttle” valve may be disposed in the hydraulic line to adjust the total movement (lift) and movement speed of the ICE valve, as the ICE valve moves from open to closed and vice versa. Dampening the hydraulically operated ICE valves can only be achieved by utilizing a complex means to attempt such dampening.
Pneumatic means have also been proposed to actuate the valves independent of the ICE crankshaft position. The systems typically use air directed through electrically operated control valves to push the ICE valves open and shut. A major drawback of such systems is that the ICE valves slam into their limit stops upon opening and also slam into the valve seats upon closing. Such slamming causes mechanical damage to the valves fairly quickly. In some cases springs and other mechanisms have been added to cushion the valves, but these add significant complexity to the valve system.
Yet another attempt to resolve the deficiencies of camshaft-operated valves has been to electrically operate the valves using computer control with some form of solenoid for valve actuation and also a dampening means. A solenoid operates by fully opening and fully closing the device that it acts upon. Solenoids cannot be controlled to move at a variable rate or to vary speed upon opening/closing or to vary opening movement distance (lift). The only way to vary the rate of opening, stopping, closing or movement distance (lift) in a solenoid operated system is with external mechanical devices, which add to the overall complexity of the system. The solenoid arrangement and drawbacks can be understood with reference to examples thereof. Both mechanical springs and fluid shock absorbers have been proposed as cushioning mechanisms None of these have offered any technique for variable lift which is preferable to facilitate easy starting, idling and low speed operation. The dampening techniques proposed are also complex and raise reliability concerns. Some use two solenoids formed on the ICE valve stem, one to open and one to close the valve with the addition of springs on the valve to hold the valve in a nominally closed position. No provision is provided by these inventions for variable lift adjustment of the valve.
Due to the deficiencies of these prior attempts, there remains a need to provide a valve actuation system, method and device for ICEs that reduces cost, weight and complexity, while providing for fully independent control of the valve actuation parameters.